The propeller screw and its many modifications form the basis of most current propulsion systems. Design and manufacture of the propeller screw requires mastery of foil dynamics in which profile, shape, area, angle, number of blades, and speed are important parameters. Moreover, the phenomena of cavitation and stall limit the performance of the majority of propeller screws. Propeller screws are also sometimes lethal to wildlife.
There is an effort to develop alternative propulsion systems in the form of reciprocating wings, with a promise of greater efficiency. Most engines in use today are of the reciprocating type, yet they are invariably used in rotary mode; the mechanical simplification afforded by direct drive of oscillating propulsion systems would be a major advantage. Reciprocating propulsion systems may also be better suited to harnessing wave power for propulsion, further increasing efficiency and helping to preserve the environment through reduced hydrocarbon use. However, current reciprocating propulsion systems are still based mostly on the airfoil or hydrofoil concept and can be expected to suffer from some of the limitations of the propeller screw, as already outlined.
A different approach to fluid propulsion involves imparting energy to a contained volume of fluid before discharge; other than enclosed propellers it appears that piston and diaphragm pumps, and the likes are the existing alternatives, with limited market success in craft propulsion. A submersible buoyant cup with transverse opening is disclosed in U.S. Pat. No. 3,236,203 to Bramson (1966): this design is based on raising a volume of water in the cup from a body of water to a height above the body of water for release under the influence of gravity. Drainage of water from the cup imparts a reaction force to the cup. Thrust from Bramson (1966) device is limited by the gravity of the Earth, a relatively constant force. The potential power of this design is also limited by the diameter of the cup, since discharge of water at a height greater than the diameter of the cup may not add substantially to propulsion; the cup would start discharging its content as soon as it emerges from the water body and would be completing its discharge by the time the whole cup is out of the water body, depending off course on the dimensions of the cup. On the other hand, the time required to fill the cup under water would also be similarly limited by the cup dimensions and the potential for air entrapment within the cup. The above limitations imply a maximum stroke rate and speed for the device, governed by cup dimensions, geometry, gravity, and fluiddynamics considerations. Bramson (1966) propulsion device must surface to produce thrust. To this end the geometry and buoyancy of the cup are for water retention and conveyance to the surface and not for submerged operation. The need to surface also reduces efficiency since thrust would be produced mostly at the end of the upward stroke, as water egresses from the cup.
The novel oscillating propulsor of the present disclosure can operate partially or fully submerged. The unique geometry and operation of the oscillating propulsor provide for cyclic acceleration and ejection of a volume of fluid to produce thrust and enable displacement. Other objects and advantages of my invention will become apparent from the detailed description that follows and upon reference to the drawings.